A super PAC run by Gabrielle Giffords and her husband, Mark Kelly, has about $9 million in cash on hand. / Valerie Macon, Getty Images

by Fredreka Schouten and Christopher Schnaars, USA TODAY

by Fredreka Schouten and Christopher Schnaars, USA TODAY

WASHINGTON - Democratic-aligned super PACs headed into the summer with a more than 2-to-1 cash advantage over Republican political action committees, many of which spent heavily on bruising Senate primaries, a USA TODAY review of the latest federal campaign reports shows.

Liberal-leaning groups account for four of the five groups with the biggest bank accounts to date.

The analysis looked at the balance sheets of super PACs that have collected at least $100,000.

Former congresswoman Gabrielle Giffords' gun-control PAC has amassed the biggest war chest of the groups examined. The Democrat's political action committee, Americans for Responsible Solutions, ended June with more than $9 million in cash reserves.

It has pledged to help candidates, regardless of party, who want to rein in gun violence. Six of the seven Senate contenders it is backing are Democrats in races that will decide which party controls the chamber next year.

Republicans must net six seats to win the Senate in November.

GOP-aligned establishment groups have paid a high price to quell Tea Party-fueled insurgencies in a series of highly contentious primaries this year. American Crossroads, a super PAC affiliated with Republican strategist Karl Rove, pumped $1.6 million into a single race to help Thom Tillis, North Carolina's House speaker, fend off challenges from a welter of other GOP candidates.

The spending was worth it, the group's leaders say.

"Our strategy in engaging in primaries in this cycle has delivered a stronger return on investment," said Paul Lindsay, Crossroads' spokesman. "Part of it is ensuring that the most electable Republican candidate won the primary. The other advantage is using the opportunity to start defining the Democratic candidates early."

American Crossroads had $4.6 million in cash reserves at the end of May, its most recent filing shows. Senate Majority PAC, working to elect Democrats to the Senate in November, ended May with far more money, nearly $7.1 million.

The Democratic group has spent more than $19 million on Senate races - all of it trained on general election battles, according to a tally by the Center for Responsive Politics, which tracks political spending.

"We haven't faced these bitter, divisive primaries," said Ty Matsdorf, a spokesman for the Senate Majority PAC. "We have been very fortunate that since the beginning of the cycle, we have been focused on November."

Individual Democratic candidates in key Senate races also are showing fundraising strength as the election season gets underway.

Sen. Kay Hagan, D-N.C., a top target for Republicans, raised $3.6 million from April to June and stockpiled $8.7 million in cash reserves. Tillis, her GOP rival, ended June with $1.5 million in available cash.

The primary season for Republicans isn't over. There are Senate contests still to come in Tennessee, Alaska, Kansas and Georgia, where Tuesday's runoff will pick the Republican vying to replace retiring GOP Sen. Saxby Chambliss.

As Georgia's primary battle has dragged on, the Democrats' nominee, Michelle Nunn, has filled her bank account. She collected nearly $3.5 million from April to June, her campaign said.

No matter how much cash their candidates squirrel away, Democrats expect to be vastly outspent by outside groups, particularly non-profit organizations that are active in politics but do not disclose the details of their fundraising nor their funders.

Crossroads plans a $20 million TV advertising blitz in six Senate battlegrounds this fall. Its non-profit arm, Crossroads GPS, will pick up about half the costs.

Americans for Prosperity, a non-profit group tied to conservative billionaires Charles and David Koch, has indicated it may spend $125 million this year. A recent analysis by the non-profit Sunlight Foundation found that Koch-affiliated groups bought ad time at more than 100 television stations across the country.